This invention relates generally to the field of optical communication systems and specifically to determining a protection path through an Wave Division Multiplexing (WDM) network.
The popularity of the Internet has created a deluge of data traffic. The data traffic may force service providers to consider new infrastructures that meet the explosive demand for bandwidth. Wavelength Division Multiplexing (WDM), which allows a single fiber to carry multiple signals simultaneously, is perceived to be a promising candidate to address the bandwidth shortage on the Internet. While the enormous amount of bandwidth provided by WDM may help alleviate the mounting pressure for higher access speed, it also makes protection/restoration a very important issue in network management. For example, current technology allows up to 128 wavelengths to be multiplexed in a single fiber, each with a data rate up to 10 Gbps. This roughly translates into millions of telephone calls on a single fiber. Hence it is easy to comprehend the catastrophic consequence a fiber cut may cause without an appropriate protection mechanism in place.
Different types of protection schemes have been developed for optical networks. Many existing transport networks use Synchronous Optical NETwork (SONET) rings. SONET rings are simple topologies which contain two separate paths between any pair of nodes which are resilient to any single link or node failures. Although simple and fast, the direct application of the ring architectures in WDM networks brings a number of problems. It is well known that ring-structured protection schemes typically rely on excessive capacity redundancy. By contract, one can provide protection with substantially less spare capacity on mesh optical networks. The protection schemes on mesh optical networks were intensively studied in the early 1990s. Nevertheless, mesh-based SONET is not widely used due to certain inadequacies, notably the slow restoration process that sometimes takes more than 2 seconds.
Typical Digital Cross-Connect Systems (DCSs) in transport networks have very limited functionality. Hence only simple restoration algorithms were previously developed for mesh networks. Recently the emerging use of Optical Cross Connects (OXCs) on WDM networks are shedding new light on the survivability issues of mesh networks. Intelligent OXCs, unlike their predecessor DCSs, function much more like Asynchronous Transfer Mode (ATM) switches or Internet Protocol (IP) routers. OXCs offer dynamic configuration via light path switching and allow many management tasks to be carried out in a distributed manner. Because of the dominance of IP traffic, IP-oriented control plane are being considered for WDM-based optical networks in order to provide seamless data transport. The goal is to provide integrated functions such as light path routing, signaling, and restoration. This brings forth a significant shift in the management paradigm from centralized control to distributed control. This shift in management paradigm has significant impact on the design of protection solutions for WDM networks.
Two major issues of network survivability/restoration, namely time and resource efficiency, now can be addressed separately. Restoration may be handled in two phases, planning and activation. Resource efficiency is optimized during the planning stage with restoration speed being optimized during the activation phase. At the planning phase, protection light paths are pre-computed and stored in OXCs before failures occur. At the activation phase when actual failure occurs, OXCs switch to pre-determined protection light paths. Thus traffic can be re-routed promptly in real time.
Most of the previously proposed solutions to optimize resource utilization in survivable mesh networks assumed that complete information about traffic demands is known a priori. Therefore, the protection paths for these demands were computed in a batch, either in a centralized manner or through distributed algorithms. The batch computation may work well in conventional telecommunication networks where the traffic demand is relatively static, but batch computations are not suitable in a dynamic, data-centric environment such as the bandwidth-on-demand paradigm now considered by Optical Domain Service Interconnect (ODSI) and Internet Engineering Task Force (IETF). With batch computation, any incremental changes of traffic demand may cause every existing path to be re-computed, which is not desirable.
The existing methods to restore path computation can be roughly categorized into either path-based or link-based approaches. In the former case, upon the detection of the failure event by the destination node of the connection, a notification is sent to the traffic source where the backup path is activated. In the latter case a failure event is detected and dealt with locally, i.e., a “detour” is set up around the failed link/node.
On the one hand, a path-based approach benefits from its ability to create a resource-efficient backup path, but it incurs longer response time. On the other hand, link-based approach may not be able to establish the “optimal” protection path, but the speed at which a backup path is set up is much higher.